Identifying Atomic-Level Correlation between Geometric and Electronic Structure at a Metal–Organic Interface

The interface of π-conjugated organic molecules with metal surfaces plays a crucial role in determining the efficiency of organic-based electronic devices. Because the interface is buried under the molecule, it is often experimentally inaccessible. Here, we propose a way of simultaneous structural and electronic characterization of the interface of the metal–organic system. Using the molecular manipulation technique of scanning tunneling microscope, we conducted a systematic study of geometric and electronic structure on the same footing and identified the atomic-scale correlation between them for copper phthalocyanine molecule on the Au(110). The energy level of the lowest-unoccupied molecular orbital (LUMO) is found to be linked with the number of underlying Au atoms (n = 2–10) at the interface. The LUMO decreases with n in energy and reaches close to the Fermi level, demonstrating explicitly that the electronic property of the molecule is affected by the atomic-scale variation of the interface. The density functional theory calculations reproduced the energy-level shift as a function of n and identified the origin of the correlation.